Fluid-pressure machines



3, 1965 A. CAMERON-JOHNSON 3,198,129

FLUID-PRESSURE MACHINES Filed Sept. 25. 1962 1; FIG].

24 23 26 28 29 20749 l8 l5 l7 ll I4 IN VE r17? K ALAA/ CAMENN-TMNSON ,4 77-012 EYs United States Patent 3,198,129 FLUiD-PRESSURE MACHINES Alan 'CameronJohnson, Cheltenham, England, assignor to Dowty Rotol Limited, Cheltenham, England, a British company Filed Sept. 25, 1962, Ser. No. 226,104 Claims priority, application Great Britain, Sept. 29, 1961, 35,286/ 61 1 Claim. (Cl. 103-162) This invention relates to axial piston fluid-pressure machines which can be used as pumps or which can be used as motors. In such machines there is provided a plate in engagement with the pistons, the angle of inclination of the plate with respect to the pistons being such that relative rotation between the plate and the ends of the pistons engaging the plate elfects reciprocation of the pistons. The plate may be arranged for adjustment of its angle of inclination with respect to the pistons so as to vary the stroke of the pistons.

According to the invention there is provided an axial piston fluid-pressure machine in which the fluid capacity of the machine is adjustable by means of a double-wedge assembly, one part of which assembly can be angularly adjusted so as to cause tilting to a greater or lesser degree of the other part of the assembly.

Also, according to the invention, there is provided an axial piston fluid-pressure machine having a barrel, cylinders in the barrel, pistons reciprocable in the cylinders, a plate co-operable with the ends of the pistons without the cylinders, the angle of inclination of the axis of the plate with respect to the axis of the barrel being variable by cooperating wedge-shaped members, one of which is angularly adjustable and the other of which is non-rotatable but tiltable about an axis which is substantially transverse with respect to the axis of the barrel.

The angularly adjustable wedge-shaped member may be of ring shape and be supported for rotation in the casing of the machine in a first bearing whose rotational axis is coincident with the axis of the barrel, the other wedge-shaped member engaging the angularly adjustable wedge-shaped member through the intermediary of a second bearing.

By the invention, the relatively large trunnion mountings which have hitherto been necessary for pivotally mounting the swash plates of conventional adjustable mechanisms can be dispensed with and a more compact means of tilting the swash plate afforded. Thus a fluidpressure machine generally of more compact form is pro vided.

One embodiment of the invention will now be particularly described by way of example with reference to the accompanying drawings, of which,

FIGURE 1 shows in axial-section a fluid pressure machine according to the invention constituting an hydraulic pump, and

FIGURE 2 shows a part-cross-section on FIGURE 1 taken along the line IIII.

The hydraulic pump shown by way of example comprises a casing 11 having an inlet 12 and an outlet 13, the casing supporting a rotatable cylinder barrel 14 in suitable bearings. The barrel 14 is provided with a number of circumferentially-spaced cylinders 15 which are parallel to the rotational axes 16 of the barrel 14. Each cylinder 15 is provided with a piston 17 reciprocable therein. The outer end portion 18 of each piston, that is the end portion to the left of the piston in FIGURE 1 of the drawing, fits into a slipper 19 which in turn engages a plate 20 hereinafter referred to as a swash plate. A driving shaft 21 for effecting rotation of the cylinder barrel 14 passes through the centre of the pump casing 11 and is a splined fit at 22 with the cylinder barrel.

3,198,129 Patented Aug. 3, 1965 A first wedge-shaped member 23 of ring shape is supported in a first double ball bearing 24 located between abutments 25 and 26 in the casing 11 of the pump, the inner races of the bearing 24 being formed in the member 23. The member 23 is angularly adjustable in the double ball bearing by a power motor in the form of a small hydraulically operable jack 27 which is transversely mounted within the pump casing 11. The member 23 is formed integrally with a pair of outer races 28 and 29 of a second double ball bearing 30. The plane of this bearing is inclined with respect to that of the first double ball bearing 24. The inner races 31 and 32 or" the second double ball bearing 30 are retained by a locking ring 33 upon a cylindrical extension 34 of the swash plate 20, this extension projecting in a direction away from the pistons 17 from the swash plate. The swash plate 21! and the integral cylindrical extension 34 effectively contitute a second wedge-shaped member which is in engagement through the intermediary of the double ball bearing 30 with the first wedge-shaped member 23. Thus the member 23, cylindrical extension 34, swash plate 20 and bearings 24 and 30 together form a double-wedge assembly.

As will be seen from FIGURE 2, the second wedgeshaped member 20, 34, is constrained against rotation by means of a radially-disposed peg 35 which engages the casing 11 of the pump. The plane containing the peg 35 passes geometrically through the point of intersection of the rotational axis 16 with the axis of rotation of the second double ball bearing 30. The plane containing the centres of the ball ends 18 of the pistons 17 also passes through this point of intersection.

In operation, the jack 27 is operated manually, or, preferably, automatically in accordance with the delivery pressure of the pump so as to oil-load the pump when required. Such operation of the jack 27 effects angular adjustment of the first wedge-shaped member 23 in the first double ball bearing 24. In consequence the second Wedge-shaped member 26, 34, is accordingly caused to tilt to vary its angle of inclination with respect to the rotational axis 16 of the pump. In this way the stroke of the pistons 17 is varied in accordance with requirements.

It has been found with my invention that the most favourable condition for achieving a change of angle of the swash plate face with the minimum parasitic movement in a plane at right-angles to the principal tilt is achieved when the longitudinal plane through the line of maximum inclination of the first wedge-shaped member 23 is angularly adjusted, during the tilting of the swash plate from Zero to maximum, through an angle bisected by the longitudinal plane through the transverse axis about which the swash plate is tilted.

Conventional variable-angle swash plate-type pumps have the disadvantage of an inherent fluctuating torque around the trunnion axis of the swash plate due to the pistons changing from an unloaded to a loaded state and back successively as they pass their inner and outer dead centre positions. This torque has normally to be reacted by the control mechanism governing the swash plate angle. However, in a pump in accordance with the invention this torque is reacted directly into the structure of the machine through the double-wedge assembly.

Although in the embodiment described, the jack 27 is operated automatically, in an alternative embodiment of the invention this jack is operated by a manual control.

Although the invention has been described as applying in the control of a variable delivery-hydraulic pump, within the scope of the invention the principle may be applied to the control of other similar fluid-pressure machines which employ swash plates, or the like, of variable inclination, for example, hydraulic motors.

Iclaimas my invention: A variable capacity fluid-pressurermachine comprising a casing and a barrel rotatable therein about a fixed axis,

and formed with a plurality of circumferentially spaced, axially directed cylinders,

cylinder, a swash plate whereon the projecting end, of each piston bears,

second wedge-shaped member forming the otherv part of the double-wedge assembly, and including said swash plate, said second wedge-shaped member being supported from the casing for tilting movement abouta tilting axis disposed substantially transversely of the machine and intersecting the fixed axis,

a piston reciprocable in each a first wedge-shaped member forming, one part of a double-wedge assembly, and mounted in said casing for angular adjustment about such fixed axis, a a

but constrained against rota tion, and the two wedge-shaped members being inter connected for their relative angular movement about an axis which intersects the fixed axis at the intersection of I t 1;; I v the latter and the tilting'-axis,and means to: adjust said first wedge-shaped member about the fixed axis, whereby the resultant tilting of thesecond wedge-shaped member will efiect adjustment of the angle of the swash plate about the tilting axis, and consequently of the stroke of the pistons within their cylinders.

7 References Cited bythe Examiner UNITED STAT ES PATENTS LAURENCE v. EFNER, P1-imary Examiner. 

